The present invention relates to an improved physical stabilization of aqueous solutions of homopolymers and copolymers of N-vinylpyrrolidone with hydrogen peroxide, and to a method of producing such solutions.
Homopolymers and copolymers of N-vinylpyrrolidone are used for a large number of applications in the form of their aqueous solutions. Such solutions are generally stored by the user for a certain time. This requires stabilization with regard to the physical properties of the solutions, i.e. with regard to odor, color, opacity. Stabilization with regard to the viscosity is also important for the application properties of such solutions. An important aspect of the stabilization here is also stabilization against short-term thermal stresses. Thermal stresses can, for example, lead to the color being impaired, which is evident from an increase in the iodine color number. In addition, even after further working the polymer solutions to give aqueous systems such as, for example, gels, the physical stability of the polymers should be ensured without resulting in the properties of the secondary products being adversely affected. At the same time, such solutions must, however, also be protected against bacterial attack.
The use of hydrogen peroxide with N-vinylpyrrolidone homopolymers or copolymers in aqueous solutions for producing complexes for disinfectants is known per se. For this, firstly solutions of the polymers with H2O2 are prepared, which are then converted to the pulverulent complexes. Such products comprise complex-bound hydrogen peroxide in the percentage range. Such complexes are described, for example, in DE-A 43 44 131.
However, it was feared that the use of hydrogen peroxide in solutions of corresponding polymers could lead to the crosslinking of these polymers since hydrogen peroxide is also used for producing crosslinked PVP. Thus, it is known, for example, from WO 98/58990 that polyvinylpyrrolidone can be crosslinked with hydrogen peroxide.
Furthermore, it is known that aqueous solutions of such polymers can be stabilized with alkyl parabens. Although such parabens are approved for applications such as, for example, cosmetics, they also have applications-related disadvantages. Particularly with low molecular weight VP polymers, compatibility is low. Furthermore, turbidity has been observed, meaning that products stabilized in this way do not appear to be suitable for applications such as, for example, hair gels. Added to this is the fact that such compositions often have to be used for effective stabilization in amounts in the percentage range and furthermore are present in the end product in unchanged amounts. Allergic reactions to such compositions can also not be ruled out.